Method and apparatus for measuring absolute densities

ABSTRACT

Disclosed herein is a method and an apparatus for measuring the absolute densities of fluids. The apparatus includes a sample cup and a sealing cap with a valve therein through which the cup can be charged with fluid to be measured. A pressure pump and weighing device are also disclosed with which the cup is charged and weighed.

1451 July 24,1973

United States Patent 11 1 Nickles et al.

8/1932 Mott et I m V. mm m ho mSPH 84 64 3556 9999 1111 l/l/ 0254 156245 738800 12769 73642 12223 METHOD AND APPARATUS FOR MEASURINGABSOLUTE DENSITIES [75] Inventors: Stephen K. Nickles; Joel M. Stogner,

both of Duncan, Ok1a.; James L. Doerksen, Monahans, Tex.

1,089,674 11/1967 United Kingdom.........,........... 73/32 [73]Assignee: Halliburton Company, Duncan,

Okla.

[22] Filed: Al": 7 1971 Primary ExaminerRichard C. Queisser AssistantExaminer-Arthur E. Korkosz [21] Appl. No.: 131,963

Attorney-John H. Tregoning, Michael J. (addell etal.

[57] ABSTRACT Disclosed herein is a method and an apparatus formeasuring the absolute densities of fluids. The apparatus 82 3 30 8 39 74 18 2 U HG 3 3 7 "M3 M74 mmm9 m m mmm m me W W W8 m"& um C smfw UIF 1]]218 555 includes a sample cup and a sealing cap with a valve [56]Reference Cit d therein through which the cup can be charged with UNITEDSTATES PATENTS fluid to be measured. A pressure pump and weighing deviceare also disclosed with which the cup is charged and weighed.

2,668,437 2/1954 73/19 1,229,641 6/1917Munzner................,.......... 73/433 X 6 Claims, 6 Drawing FiguresPAIENIEU 3.747. 415

sum 1 0r 3 2r 5 60 I6 26 4O 102 Ill P41 107 FIGURE 1.

114 INVENTORS Stephen K. Nickles James L. Doerksen FIGURE 2. zL gler cATTOR Y Pmmnnmz 3347.415

SHEET 2 0F 3 LL] 0: D Q I L.

FIGURE 30.

@Immmn I NVENTORS Stephen K. Nickles James L. Doerksen Joel M. SfognerMM (9M ATTORN PATENIED SHEET 3 [IF 3 FIGURE 4.

mmm W am". Emm mK fimf he v p I. mmuflmm SJJ m T Y T B A I O 1 H METHODAND APPARATUS FOR MEASURING ABSOLUTE DENSITIES BACKGROUND OF THEINVENTION In the drilling of oil wells, drilling fluid, called mud, isused to cool and lubricate the drilling bit and to remove rock fragmentscut by the bit. It is very important to know at all times the density ofthe mud being pumped into the well; for example, if the density is toolow, and the drill bit hits a high pressure oil and/or gas zone, ablowout may quickly develop, destroying the drilling rig and injuringand/or taking the lives of the drillers. On the other hand, if the muddensity is too high and the bit hits a low pressure or thief zone,

thousands of dollars of expensive drilling mud can be quickly lost tothe formation.

Various devices are used in determining densities in the oil fields withthe mud balance" being the most common. The mud balance consists of abase and graduated arm with cup, lid, knife edge, sliding weight, spiritlevel, and counterweight. The cup, having a constant volume, is affixedto one end of the graduated arm and the counterweight on the oppositeend. In operation, the cup is filled with mud, and the density, inpounds per gallon, is measured by sliding the weight along the graduatedarm until the arm is equally balanced on both sides of the knife edge. Amajor problem which is associated with the density measurements obtainedin the manner described above is that often times the fluid beingmeasured contains a considerable amount of entrained air. Thus, themeasured density is in error by the amount of air or gas containedin thesample.

The present invention provides an apparatus for measuring absolutedensity of a fluid which comprises a container having an opening, acover adapted to close said opening on said container, valve means onsaid cover for admitting fluid into said container through said cover,and means for securing said cover to said container. r

In order to more fully describe the present invention reference is madeto the following drawings wherein:

FIG. 1 illustrates a test chamber involving features of the presentinvention;

FIG. 1a is a cross-sectional view of the valve of FIG.

FIG. 2 illustrates the test chamber with a pressuring pump attached;

FIG. 3 illustrates the test chamber attached to a weighing instrument;

FIG. 3a is a top view of the weighing instrument of FIG. 3; and

FIG. 4 illustrates a different embodiment of the invention shown in FIG.1.

DETAILED DESCRIPTION OF THE EMBODIMENT OF FIG. 1

FIG. 1 illustrates test chamber 10. Chamber includes cup 12 which holdsthe sample of fluid to be weighed. An opening 14 in cup 12 is closed bysealing cap 16 whose outward extending flange l8 rests on edge 20 of cup12. Surface 21 of cap 16 contains a raised inner platform 22. Extendingdownward on cap 16 is skirt 23. An O-ring 24, positioned on skirt 23,provides sealing means between cap 16 and cup 12. Parenthetically, allO-rings referred to herein, such as ring 24, are seated in appropriaterecesses in accordance with standard practice in connection with suchdevices.

A centrally positioned passageway 26 extending through inner platform 22is provided to receive pressuring valve 28 whose function will bediscussed later. Referring to FIG. la, valve 28 consists of an elongatedbody 30 having on its lower end 32 a flange 34 disposed in a planeperpendicular to the axis of valve 28. Lower O-ring 36 encircles body 30directly above flange 34 and provides sealing means between valve 28 andthe walls of passageway 26. The upper end of body 30 is designated at38. Positioned between lower end 32 and upper end 38 is outwardlyprojecting lock ring 40 which prevents valve 28 from falling or frombeing pushed down through passageway 26 by catching on platform 22 ofcap 16.

The upper half of valve 28, designated by the letter A, extending fromslightly above lock ring 40 to upper end 38, is of less diameter thanthe lower half of valve 28, designated by the letter B, except for alaterally extending'ledge 44 located midway between upper end 38 andring 40. A recess 45 is defined by ledge 44 and the top of the bottomhalf of valve body 30. The function of ledge 44 and recess 45 will beexplained below.

An upper O-ring 46 is positioned just below upper end 38. Its functionwill be discussed later.

Valve 28 contains central passageway 47 which begins at the face ofupper end 38, extends axially downwardly and terminates within body 30.At the point of termination, designated at 48, central passageway 47divides into two or more lateral passageways collectively number 50.Passageways 50, spaced equidistance one from the other, extend outwardlyperpendicular to the axis of valve 28, emerging on the surface of body30 slightly above O-ring 36. These places of emergence are collectivelynumbered 52.

Returning to FIG. 1, a ferrule 56, adapted to be attached to cup 12 viacompanion threads 58, has an inwardly projecting flange 60. As shown inFIG. 1, flange 60 bears on cap surface 21 and holds cap flange 18vagainst cup edge 20 at a fixed point so that the volume of cup 12 isalways constant.

Referring now to FIG. 2, test chamber 10 is shown attached to pressuringpump 70. Pump consists of a housing 72 that has upper end 74, lower end76, and passage 78 extending axially therethrough.

A piston assembly 80 includes a piston rod 82 with a handle 84 at upperend 85 and a piston head 86 adjacent to lower end 88. Rod 82 and pistonhead 86 are adapted for reciprocal motion within passage 78 of housing72. A fluid sealing element 90 provides a seal between piston head 86and inner walls 92 of housing 72.

Rod guide 96, attached to housing 72 at upper end 74 via companionthreads 98, has an inwardly extending flange 99 which defines a bore 100whose diameter is slightly larger than the diameter of rod 82 andslightly less than the diameter of piston head 86. Flange 99 keeps rod82 axially centered within passage 78 during reciprocal motion, and alsoprevents withdrawal of piston assembly 80 from housing 72 by retainingpiston head 86 within passage 78.

A valve coupler 102 is attached to the lower end 76 of housing 72 viacompanion threads 104. A passageway 106 extends axially through coupler102. As shown in FIG. 2, the passageway 106 is formed to have threeconcentric bores; upper bore 107, center bore 108, and lower bore 109.As explained above, lower end 76 of 7 whose absolute density is to bemeasured as will be explained later. Entrained air in fluid 112 isdesignated at 114.

FIG. 3 illustrates the balancing instrument 120 designed for use withtest chamber 10. The instrument 120 includes a mounting base 122 whichholds a knife edge 124 on top thereof. Resting on knife edge 124 ispivot 126 which has been partially sectioned to show spirit level 128positioned within. Window 130 on top of pivot 126 allows visualobservation of level 128. A beam 132, graduated for use with chamber 10,passes through and is rigidly attached to pivot 126. At the right end133 of beam 132 counter-weight 134 is attached. Between pivot 126 andcounter-weight 134 and riding on beam 132 is sliding weight 136 whichhas an arrow 137 inscribed thereon. The purpose of arrow 137 thereonwill be explained later.

The left end of beam 132, designated at 138, is adapted to receivechamber 10. The thickness of the beam at left end 138 is reduced to beslightly less than the width of recess 45 on valve 28. A slot 140, whichcan be seen in FIG. 3a, is provided on end 138 which results in theformation of two arms, collectively numbered 142. At the terminal end ofslot 140, a semicircular recess 144 is provided. Test chamber 10 isplaced on instrument 120 by placing recess 45 between the two arms 142and sliding chamber 10 along slot 140 to where it drops down into recess144.

FIG. 3a also shows window 130 on pivot 126, sliding weight 136, and thepoint of attachement for counterweight 134. In addition to the parts ofinstrument 120, FIG. 3 and FIG. 3a illustrate the graduated beam 132.Note that one side of beam 132, shown in FIG. 3, is calibrated tomeasure density in pounds per cubic foot. The top of beam 132, shown inFIG. 3a, is calibrated to measure density in pounds per gallon. Theopposite side of beam 132 (not shown) is calibrated to measure specificgravity. The operation of instrument 120 will be discussed furtherbelow.

OPERATION OF THE EMBODIMENT OF FIG 1 When it is desired to determine thedensity of fluid I12, cup 11 is filled with fluid 112 containingentrained air 114, from some source such asthe mud pit; cap 16 is placedon top of cup 12 and ferrule 56 is attached to cup 12, securing cap 16thereto. Pressuring pump 70, loaded with fluid 112 from the same source,is then coupled to chamber 10 by sliding lower bore 109 of coupler 102onto the upper half of valve 28 until further movement is arrested byridge 46 on valve body 30. FIG. 2 illustrates the attachment of pump 70to chamber 10.

A force is now exerted downwardly by hand both on housing 72 and onpiston rod handle 84. The force on housing 72 pushes valve 28 downwardlythrough cap 16 until lock ring 40 arrests further movement by engagingplatform 22 on cap 16. At this point passageways 50 open into cup 12.The force on handle 84 causes piston rod 82 and piston head 86 to movedownwardly through passageway 78 pushing fluid 112 into cup 12. This iscontinued until no more fluid can be forced into cup 12. As the force isreleased from housing 72 and handle 84, valve 28 is forced upward by thepressure of fluid 112 within cup 12 so that passageways 50 are sealedfrom the cup by O-ring 36 contacting the walls of passageway 26. At thispoint all entrained air 114 within cup 12 has been compressed to anegligible volume. Chamber 10, with pump removed from engagementtherewith, is placed into recess 144 on left end 138 of beam 132 ofinstrument for weighting as shown in FIG. 3. Sliding weight 136 is movedleft or right until the bubble within spirit level 128 is centered,indicating that test chamber 10 on the left of pivot 126 is preciselybalanced by counter-weight 134 and sliding weight 136 on the right ofpivot 126. Reading graduated arm 132 immediately to the side of weight136 to which arrow 137 points, the absolute density of fluid 112 isfound.

DESCRIPTION OF THE EMBODIMENT OF FIG. 4

FIG. 4 illustrates a different embodiment of the instant invention. Thisembodiment permits the measurement of the absolute volume of a fluid ormaterial from which the absolute density may be obtained. Test chamber10' is identical to chamber 10 shown in FIGS. l-3 except that valve 28has been replaced by a conventional tubing connector attached to sealingcap 16'. Cup 12 and ferrule 56' of FIG. 4 are the same as cup 12 andferrule 56 of FIGS. l-3.

Instead ofa pressure pump 70 (FIG. 2) and a balancing instrument 120(FIG. 3), the measuring equipment used with chamber 10' includes acalibrated air fixed volume cell 152, a pressurized air supply tank 154,pressure gauge 156, two valves 158 and 160, and several pieces oftubing, collectively numbered 162, which connect the above pieces ofequipment to each other and to chamber 10 in an arrangement as will nowbe explained. Cell 152 is connected on one side to tank 154 with valve158 interposed as shown in FIG. 4. On its other side, cell 152 isconnected to chamber 10, via coupling 150, with valve 160 intervening.Pressure gauge 156 is placed on tubing 162 between cell 152 and valve160.

Tank 154 may be secured to platform 164 via bolts 166.

OPERATION OF THE EMBODIMENT OF FIG. 4

Cup 12' is filled with a sample of any kind of material or fluid (notshown) which may and generally does contain some entrained air. Sealinglid 16' and ferrule 56' are fixed to cup 12'. Chamber 10', its contentsbeing at atmospheric pressure, is attached via coupler 150 to valve 160which is closed as is valve 158. After making the above connection,valve 158, between cell l52and tank 154, is opened and cell 152 ischarged with air from tank 154 to some desired pressure P, which isobserved on pressure gauge 156. Valve 158 is closed and valve 160 isopened permitting the air in cell 152, which is at a pressure greaterthan atmospheric, to flow into test chamber 10'. The volume of air fromfixed volume cell 152 entering chamber 10' will be reflected by areduced pressure reading on gauge 156. Taking this pressure, designatedas P,, and the initial pressure, P,-, the absolute volume of the samplecan be computed by using the following formula:

V,, V V, V,, (P /P where:

V, absolute volume of the sample V, volume of cup 12 V, volume of cell152 P, gauge pressure of cell 152 before opening valve P,= gaugepressure of cell 152 and chamber after opening valve 160 As an exampleof this operation, assume the volume of cup 12 to be cubic inches, thevolume of cell 152 to be 5 cubic inches and the following pressuresobserved on gauge 156:

P, 20 pounds per square inch gauge P,= 10 pounds per square inch gaugeUsing these values in the above equation we obtain:

V 20 in 5 in 5 in (20 psig/lO psig) and we find that the absolute volumeof the sample is l5 cubic inches. If desired, the absolute density canthen be determined by simply weighing the same sample and dividing thatweight by the absolute volume.

The above calculations can be avoided by using a pressure gauge 156whose dial face has been calibrated to read the absolute volume directafter valve 160 has been opened.

Besides determining the absolute density and volume of drilling fluids,the instant invention will find application in many other situations.One application relates to the preparation of a cement slurry used incementing a string of casing in a well bore. The density of the slurryis increased by adding barite or other similar, expensive material. Ifthe device used in measuring the density does not consider the volume ofentrained air, more weighting material will be added than is required.Not only is this an economic waste but the horsepower required to pumpthe heavier mixture will be unnecessarily increased. For example, aslurry having 10 percent by volume of air entrained will have a densityof 19.8 lb/gal if measured by a conventional mud balance and a densityof 21.9 lb/gal if measured by the present invention under a pressure of250 psig. Thus, if the desired slurry density was 19.8 lb/gal an errorof 2.1 lb/gal would have been made.

The instant invention can be constructed of various materials such asbrass, steel and the like. Two limitations exist; one is that thematerial must not react chemically with the sample being measured; thesecond limitation is that the material used must have a high enoughyield strength to withstand the pressures imposed on the test chamber.However, the second is not critical. As is well known to those skilledin the art, the higher the pressure used, the closer the value obtainedwill approach true absolute density. However, the relationship betweenpressure and absolute density is logarithmic where the true absolutedensity is approached very rapidly under modest pressures, andadditional large increases in pressures result only in very small,almost negligible changes in absolute density values. Thus it followsthat the instant invention may be practiced using light weight equipmentwhere approximate absolute densities will suffice.

Two uses have been described herein but many other uses in manyindustries will be readily apparent to those skilled in the art.

Although the invention has been described with reference to theembodiments illustrated, it will be apparent that many differentembodiments may be made without departing from the spirit and scopethereof, and therefore it is not intended to be limited except asindicated in the appended claims.

What is claimed is:

l. A method for measuring the absolute density of a fluid, whichcomprises the steps of:

a. filling a container having a cap with a valve thereon with the fluidto be measured;

b. securing said cap to said container;

c. pumping an additional quantity of said fluid into said container viasaid valve until air entrained in the fluid in said container iscompressed into a negligible volume; and

d. placing said container on an instrument calibrated to measuredensities by balancing said container against known weights.

2. In weight per unit volume measuring apparatus, a device for providingan accurate volume of fluids and semi-fluid solids having quantities ofnon-dissolved gas trapped therein, comprising:

a. container means having a closed lower end and a substantiallyunobstructed upper end;

b. closure means adapted to substantially cover said unobstructed upperend;

0. valve means in said closure means for permitting the flow of fluidtherethrough into said container means;

(1. means for removably attaching said closure means to said containermeans;

e. pump means for sealingly engaging said valve means and injectingfluid into said container at a sufficient pressure to compress saidentrapped nondissolved gases to a negligible volume;

f. valve body means slidably located within said valve means andarranged to move downward in response to fluidic pressure applied bysaid pump means and further adapted to move back upwards upon release ofsaid pumped fluid pressure; and

g. one or more bore passages in said valve body means arranged toprovide fluid communication between said pump means and said containermeans in said downward position of said valve body means, and furtherarranged in said upward position of said valve body means to preventfluid communication from said container means back into said pump means.

3. The apparatus of claim 2 further comprising means on said apparatusfor suspending said apparatus from a weighing scale; and seal meansbetween said closure means and said container means.

4. The apparatus of claim 2 wherein said container means comprises acylindrical cup having an integral closed end at the bottom and asubstantially open end at the top; and said closure means comprises aclosure cap adapted to fit snugly within said open end of saidcontainer, said closure cap having an annular outwardly extending flangeadapted to abut the upper edge of said cylindrical cup and platformmeans having opening means therein for receiving said valve means.

5. The apparatus of claim 2 wherein said attaching means comprises aninternally threaded ferrule adapted to enclose said closure cap inabutting relationship with said annular flange thereof and havingopening means therethrough for said valve means; and said attachingmeans further comprises an externally threaded portion on the upper endof said cylindrical cup adapted to matingly receive said threadedportion of said ferrule.

6. The apparatus of claim 2 wherein said pump means comprises a tubularhousing; lower valve cupler means fixedly attached to the lower end ofsaid housing and arranged to sealingly engage said valve means forfluidic communication therethrough, said coupler means having a fluidicbore passage thereconnecting rod passing therethrough.

1. A method for measuring the absolute density of a fluid, whichcomprises the steps of: a. filling a container having a cap with a valvethereon with the fluid to be measured; b. securing said cap to saidcontainer; c. pumping an additional quantity of said fluid into saidcontainer via said valve until air entrained in the fluid in saidcontainer is compressed into a negligible volume; and d. placing saidcontainer on an instrument calibrated to measure densities by balancingsaid container against known weights.
 2. In weight per unit volumemeasuring apparatus, a device for providing an accurate volume of fluidsand semi-fluid solids having quantities of non-dissolved gas trappedtherein, comprising: a. container means having a closed lower end and asubstantially unobstructed upper end; b. closure means adapted tosubstantially cover said unobstructed upper end; c. valve means in saidclosure means for permitting the flow of fluid therethrough into saidcontainer means; d. means for removably attaching said closure means tosaid container means; e. pump means for sealingly engaging said valvemeans and injecting fluid into said container at a sufficient pressureto compress said entrapped non-dissolved gases to a negligible volume;f. valve body means slidably located within said valve means andarranged to move downward in response to fluidic pressure applied bysaid pump means and further adapted to move back upwards upon release ofsaid pumped fluid pressure; and g. one or more bore passages in saidvalve body means arranged to provide fluid communication between saidpump means and said container means In said downward position of saidvalve body means, and further arranged in said upward position of saidvalve body means to prevent fluid communication from said containermeans back into said pump means.
 3. The apparatus of claim 2 furthercomprising means on said apparatus for suspending said apparatus from aweighing scale; and seal means between said closure means and saidcontainer means.
 4. The apparatus of claim 2 wherein said containermeans comprises a cylindrical cup having an integral closed end at thebottom and a substantially open end at the top; and said closure meanscomprises a closure cap adapted to fit snugly within said open end ofsaid container, said closure cap having an annular outwardly extendingflange adapted to abut the upper edge of said cylindrical cup andplatform means having opening means therein for receiving said valvemeans.
 5. The apparatus of claim 2 wherein said attaching meanscomprises an internally threaded ferrule adapted to enclose said closurecap in abutting relationship with said annular flange thereof and havingopening means therethrough for said valve means; and said attachingmeans further comprises an externally threaded portion on the upper endof said cylindrical cup adapted to matingly receive said threadedportion of said ferrule.
 6. The apparatus of claim 2 wherein said pumpmeans comprises a tubular housing; lower valve coupler means fixedlyattached to the lower end of said housing and arranged to sealinglyengage said valve means for fluidic communication therethrough, saidcoupler means having a fluidic bore passage therethrough communicatingwith the bore of said tubular housing; piston means sealingly slidablewithin said tubular body, said piston means having a connecting rodextending out of said tubular housing, and handle means connected tosaid connecting rod; and piston retaining means fixedly attached to theupper end of said tubular housing, said retaining means adapted toenclose the end of said tubular housing, and said retaining means havingan opening therethrough slightly larger than said connecting rod andarranged to have said connecting rod passing therethrough.